Ortho pseudo stereo range finder



Dec. 9, 1947. s, M, Mar :NEI LLE 2,432,432

' ORTHO PSEUDO STEREO RANGE FINDER Filed July 6, 1945 5 Sheets-Sheet 1 v v T 32 -12 26 f zs 29 STEPHEN M. MACNEILLE 5 INVENTOR WWW Dec. 9, 1947. s, MacNE[l E 4 2,432,432

ORTHO PSEUDO STEREO RANGE FINDER Filed July 6, 1.945 5 Sheets-Sheet 2 FIG.4.

. STEPHENIPLMACNEILLE INVENTOR BY WW ML, ATT'Y &AGT

Dec. 9, 1947. s. M. MacNElLLE I 2,432,432

ORTHO PSEUDO STEREO RANGE FINDER Filed July 6, l945 5 Sheets-Sheet 3 o STEPHEN M.MACNEILLE "m v INVENTOR BY WW 0 4" ATT'YAEAG'T Dec. 9, 1947. s. M. M NElLLE ORTHO PSEUDO STEREO RANGE FINDER Filed July 6, 1.945 5 Sheets-Sheet 4 FIG.9.

FIGJI.

STEPHEN M. MACNEILLE INVENTOR BY WW ATT'Y a: AG'T Patented Dec. 9, 1947 ORTHO PSEUDO STEREO RANGE FINDER Stephen M. MacNeille, Oak Ridge, Tenn., assignor to Eastman Kodak Company, Rochester, N. Y., a corporation of New Jersey Application July 6, 1945, Serial No. 603,496

8 Claims.

This invention relates to ortho-pseudo stereoscopic range finders. Such range finders are described in two of the earlier cases of this series namely, Serial No, 479,101, Mihalyi and MacNeille, filed March 13, 1943, now U. S. Patent 2,401,710, and Serial No. 526,020, MacNeille, filed March 11, 1944, now U. S. Patent 2,403,732.

It is the object of the present invention to provide an ortho-pseudo stereo range finder in which sources of error are minimized by having the beam combining system unitary in form. It is the specific object of one embodiment of the invention to provide an invert field ortho-pseudo stereo range finder. The advantages of orthopseudo systems over ordinary stereoscopic range finders and over coincidence type range finders are well known. The purpose of the present invention is to provide an arrangement which can be manufactured with great accuracy and which is capable of maintaining this accuracy even when incorporated into a long base range finder such as those used for height finders.

The present invention employs polarizing beam splitters. A Nicol prism can be arranged to act as a polarizing beam splitter and various other simple forms are known. However the most valuable form of polarizing beam splitter, especially for the present purpose is that described in my copending application, Serial No. 481,391, filed April 1, 1943, now U. S. Patent 2,403,731. In that copending application a polarizing beam splitter is made up of alternate layers of materials of high and low indices of refraction, each having an effective optical thickness at Brewsters angle of one-quarter wavelength to give constructive interference to the reflected rays. Six such layers are equivalent in polarizing power to 148 parallel glass plates separated by air.

According to the present invention an orthopseudo stereo range finder having the usual spaced viewing points, binocular viewing means and image forming means is characterized by a polarizing beam splitter positioned to receive light from each of the viewing points and to divide it into two beams polarized at right angles which for convenience may be referred to as a first beam and a second beam. The first beam from one beam splitter and the second beam from the other beam splitter are then combined to form superimposed or juxtaposed images in the image plane of one of the eyepieces. Similarly the other beams form images in the image plane of the other eyepiece. Preferably each of the beam splitters also acts as a beam combiner for receiving the second beam from the other beam splitter and combining it with its own first beam. For example, the second beams may be the transmitted ones and, for the sake of symmetry, these may be arranged to pass through a half wave retardation plate or the equivalent to rotate the plane of polarization through 90 degrees before striking the other beam splitter whereat they are reflected.

To provide an invert field, means are included in one of the beams from each beam splitter for inverting the image relative to the image formed by the other beam.

In those embodiments of the present invention in which right and left viewing point images are formed optically ahead of the central prism assembly including the polarizing beam splitters, the simplest way of providing juxtaposition of the images is to mask ofi half of each of these primary images. Thus the first beam from each of the beam splitters forms an image in one-half of the respective eyepiece image plane and due to inversion, the image formed by the second beam in each case exactly covers the other half of th eyepiece image plane.

Instead of thus masking half of the primary image plane, and in those cases where there is no primary image ahead of the central prism assembly, the juxtaposed image arrangement may be obtained very simply due to the fact that the two images reaching each image plane are polarized at right angles. This alternative employs a polarizing filter with two sections polarized at right angles for transmitting respectively the first and second beams reaching the image plane. This embodiment has the added advantage that the dividing line of the juxtaposed images depends only on the accuracy with which the filter is made and not at all on the relative setting of other optical elements.

Various specific embodiments of the invention and their relative advantages will be understood from the following detailed description when read in connection with the accompanying drawings, in which:

Figs. 1, 4, 5, and 6 are perspective views of optical systems of slightly difierent embodiments of the invention all incorporating the same central prism assembly.

Fig. 2 is a plan view of the central prism assembly employed in Figs. 1 to 6.

Fig. 3 shows the binocular field of view in an ortho-pseudo stereo range finder.

Figs. 7 and 8 are respectively a perspective View and a plan view of a slightly different central prism assembly which may be used in Figs. 1 to 5.

Fig. 9 is a perspective view of an optical system according to another embodiment of the invention.

Fig. is a plan view of the central prism assembly used in Fig. 9.

Fig. 11 is a front elevation of the same central prism assembly.

Fig. 12 is a perspective view of the optical system of still another embodiment of the invention.

Figs. 13 and 14 are respectively front and side elevations of the central prism assembly shown in Fig, 12.

In Fig. 1 light from a target being ranged is received at spaced viewing points by penta reflectors or optical squares and directed through objectives 2| which form target images in primary image planes 22. plane is masked off by an opaque area 23. Preferably the image planes 22 include field lenses as.

shown. The images thus formed are relayed by relay lenses 2 3 through a central prism assembly to eyepiece image planes 35.

The central prism assembly receives the beam from the observers left hand viewing point through one side face of a prism 25. The hypotenuse face of this prism is cemented to polarizing beam splitter 25 so that the reflected beam is polarized at right angles to the transmitted beam. The reflected beam passes from the prism 25 at normal incidence through an entrance face 34 into a complex prism having two plane reflecting surfaces 2? and as (reflecting at greater than the critical angle) and a roof surface 28 which reflects this beam through a half wave retardation plate 2S: whereby the plane of polarization of the beam is rotated through 90. The surface 21 is preferably metallized since the light strikes this surface at less than critical incidence.

The right viewing point image similarly enters a, prism 30 and is split by a polarizing beam splitter 31. Again the reflected beam traverses the half wave retardation plate 29, is reflected by the roof prism 23 and plane surfaces 34 and 21 into prism 25.

The path of the beams is most clearly illustrated in Fig. 2. The rays of light are shown by broken lines and are purposely selected slightly off-axis so as to distinguish between the two incoming beams and particularly between the four outgoing beams. In other words the rays shown do not represent the axial ray of the beams Since the plane of polarization of the reflected beam from each beam splitter has been rotated through 90 these beams will be transmitted respectively by the other beam splitter and pass through directly to the image planes 35 of the eyepieces 37 to permit binocular viewingof the images by the right and left eyes 33 and 39 of the observer. The portion of the left viewing point beam which is transmitted by the beam splitter 26 and similarly the portion of the right viewing point beam which is transmitted by the beam splitter 3i pass through quarter wave retardation plates 33 and are reflected by a total reflector 32 sandwiched between the quarter wave plates so that the beams each traverse the quarter wave plates twice, thus rotating their plane of polarization through 90. After this reflection and rotation of the plane of polarization, the beams are reflected by the polarizing beam splitters 26 and El and are combined respectively with the beams from the other viewing points as they pass through to the image planes 35. Due to the roof or dihedral reflector 28, the two images in each image plane are inverted relative to one another and due to the masks 23, these images The lower half oteach are juxtaposed. This is shown in Fig. 3 wherein the left viewing point image in the left eyepiece image plane and the right viewing point image in the right eyepiece viewing plane are shown at 40. The left viewing point image in the right eyepiece image plane and the right viewing point image in the left eyepiece image plane are shown at ll. The dividing lines 43 between the images 36 and ll correspond to the edges of the masks 23 located in the primary image planes. As shown, the erect images 40 would appear stereoscopically nearer than the invert images 4i. Adjusting means 44 is provided in one of the range finder beams for deviating the light and for rangingin the usual way,

Fig. 4 difiers from Fig, 1 by having all of the image forming system optically after the central beam splitting and combining prism assembly. This has a very valuable advantage since once the beams are combined for ortho-pseudo viewing the optical elements which act thereon are no longer critical since they act simultaneously and equally on both beams. In Fig. 4 light is received at spaced viewing points by penta prisms and 5l-and passed directly to the same central prism assembly as shown in Fig. 1, one of the beams passing through a lght deviator 44. After beam splitting and combining one pair of beams is focussed by an objective 52 in the right eyepiece image plane and the other pair of beams is focussed by an objective 53 in the left eyepiece image plane. The two images in each image plane are superimposed, one inverted relative to the other and they are polarized at right angles. In each image plane there is located a polarizing filter 54 having two sections 55 and 56 polarized at right angles as indicated by the double-headed arrows adjacent to each section. Thus the sections of the images transmitted to the eyepieces are juxtaposed again as in Fig. 3.

Fig 5 is similar to Fig. 4 but includes a system of mirrors for making that portion of the optical system which follows the central prism assembly more compact. The combined beams from each side of the central prism assembly are reflected by'front surface reflectors 60 respectively through image forming lenses BI and 82 which correspond to the objectives 52 and 53 of Fig. 4. The beams are then each twice reflected by mirrors 63 back to image planes 64 after which they are again each reflected by mirrors 65 to eyepieces 31.

Fig. 6 is a practical compromise between the arrangements shown in Figs. 1, 4, and 5. The objectives 19 are optically ahead of the combining prism, but there is no primary image ahead of the prism since the images formed by the objective 10 are in the eyepiece image planes 1|. This has the advantage of the arrangement shown in Fig. 1 in that the eyepieces are located quite close to the central prism assembly without the elaborate'mirror system of Fig. 5. It has part of the advantage of Fig. 4 to the extent that onlythe objectives are ahead of the beam splitting and combining prism.

The central prism assembly shown in Figs. '7 and 8 can replace that shown in Figs. 1 to 6 in any of the embodiments so far described. The left and right viewing point beams enter prisms l5 and 1'! respectively and are beam split by polarizing beam splitters l5 and 13 respectively. The transmitted beams in this case however, pass straight throughto strike the other beam splitter whereat they are reflected since the plane of polarizationof these transmitted beams are rotated through. by a half wave retardation 5 plate I9. Eachof the reflected rays as they first strike the beam splitters I6 and I8 pass through quarter wave retardation plates 80 to strike triple mirrors 8! whereat they are reflected and completely inverted. They then pass again through the quarter wave retardation plates 8|] so that on re-entering the prisms I5 and i1 respectively they are able to pass through the beam splitters I6 and 8 to be combined with the rays reflected I therefrom to the eyepiece. The orientation of the triple mirrors (best visualized as the corner of a cube) is not at all critical. They are shown with one side parallel to the entrance faces of the prisms i5 and ii, the edge being cut off leaving the surface 85 in each case. Similarly the top corners have been cut off leaving surfaces 84 level with the prisms l5 and Ti and .again the inside corners have been cut away leaving surfaces 83. It will be noted that small areas 82 of the quarter wave retardation plates 8!! are not covered by the triple mirror and the system may be slightly inefiicient due to this; but if the system is ob jectionable for this reason, larger triple mirrors may be used with the edges and corners cut away as in the presentcase.

Fig. 9 shows a preferred embodiment of the invention in which one of the viewing point penta prisms 90 is located effectively below and in front of the base of the range finder and the other viewing point penta prism 9| is located above and slightly behind this base line. Actually of course this oiT-setting is very slight and the equivalent effect is obtained by proper orienting of the reflectors in a symmetrical appearing housing. The right viewing point light beam enters a Porro prism 92 and is deflected from the first reflecting surface thereof to a polarizing beam splitter 93 located on the other reflecting surface of the prism. Similarly the left viewing point beam enters a Porro prism 96 and is reflected to a polarizing beam splitter 97. The two Porro prisms 92 and 96 are oriented at right angles to each other so that the beams reflected from the beam splitters 93 and 9'! are directed toward each other and because of the relative orientation of the beam splitters, these reflected beams pass respectively through the other .beam splitters to the ob jectives Hit. Those portions of the original beams transmitted by the beam splitters 93 and 9? respectively strike quarter wave retardation layers 94 and 98 and are reflected respectively by refleeting layers 95 and 99 back through the quarter wave retardation layers which results in the plane of polarization being rotated through 90. These rays are then reflected by the beam splitters Q3 and 91 and are combined with the rays which have been first reflected and then transmitted by the beam splitters. The light from the lenses 568 is reflected by mirrors l] and comes to focus in the image planes I02 in each of which a polarizing filter with two sections polarized at right angles is located. The light from the image planes is reflected by mirrors I03 through eyepieces I64 to the eyes I65. It will be noted particularly from the similarity of the plan and elevation views in Figs. 10 and 11 that the light beams travel symmetrical paths,

The embodiment shown in Fig. 12 has the right viewing point penta prism IIU effectively behind the base of the range finder and the left viewing point penta prism III effectively in front of the base. The right and left viewing point beams enter prisms I i and I IE to strike polarizing beam splitters II! and H8 respectively. As shown in Fig. 13 these polarizing beam spliters are at right angles to one another and located one behind the other. In each case the transmitted beam passes through a quarter wave retardation layer I20 and is reflected by a mirror IZI back to the beam splitters. These beams are then reflected downward by the beam splitters respectively through objectives I25 and I26. The other half of each viewing point beam is reflected upward by the beam splitters II! and H8 to a Porro prism I21 wherein they cross and are reflected downward to the other beam splitter respectively. A half wave retardation layer I28 rotates the plane of polarization of both of these second portions of the light beams so that they are oriented to pass through the beam splitters and to be combined with the first portions as reflected therefrom. The combined beams pass through the lenses I25 and I26 striking mirrors I30 so that they are directed into the image planes I3I of eyepieces I32. As before, each image plane contains a polarizing filter with sections polarized at right angles.

Having thus described various embodiments of my invention I wish to point out that it is not limited to these structures but has the scope of the appended claims.

I claim:

1. An ortho-pseudo stereoscopic range finder having spaced viewing points for receiving light from the target being ranged, two eyepieces for binocular viewing and means for directing light from each viewing point to form two images of the target being ranged in the image plane of Y each eyepiece, characterized by a polarizing beam splitter positioned to receive light from each viewing point and to divide it into a first and second beam polarized at right angles, means for directing to one eyepiece image plane the first beam from one beam splitter and the second beam from the other beam splitter, said directing means including a plurality of reflecting surfaces and each beam splitter acting as a beam combiner, combining its first beam with the second beam from the other beam splitter, a reflector positioned in each of the second means to reflect them respectively back to the beam splitters and means included in said second beams to intercept each of them twice for rotating the plane of polarization through 2. A range finder according to claim 1 in which means for inverting the image is included in one of the beams from each beam splitter.

3. A range finder according to claim 1 including means for forming .a target image between each viewing point and the corresponding beam splitter which receives light from that viewing point, means for relaying the image through the beam splitter, beam combine-r system to the eyepiece image planes and a mask covering onehalf of each of the images between the viewing points and the corresponding beam splitter.

4. A range finder according to claim 1 including in each of the eyepiece image planes a polarizing filter with two sections polarized at right angles for transmitting respectively the first and second beams reaching that image plane.

5. An ortho-pseudo stereoscopic range finder having spaced viewing points for receiving light beams from the target being ranged, two eyepieces for binocularly viewing images of the target and means for forming in the image plane'of each eyepiece two target images by lght respectively from the two viewing points characterized by a central prism assembly including a polarizing beam splitter positioned to receive light from each 7 viewing: point respectively and: ;.to form? a first beam and a second beam polarized at right angles, the-first. beamxin each. case being reflected by the beam splitter, a; plane reflector and aroof reflector, for reflecting, each of said first beamsrespem tively to the other beam splitter, a'half wave plate forrotating the plane of polarization interceptingsaid first beams so that each of the first beams will be. transmitted by said other beam splitter, the second beams inv each case being transmitted by thebeam vsplitters,,,a quarter wave retardation plate and a total reflector for receiving each of said second beams, for reflecting them back respectively toward their beam splitters and for rotating their plane of polarization through 90 degrees whereby they are reflected from the beam splitters andcombinedwith the second beams being transmittedby the beam splitters.

6. A range finder according to claim including in each of the eyepiece image planesa polarizing filter with twov sections polarized at right angles for transmitting respectively the first and second beams reaching that image plane. I

'7. An ortho-pseudo stereoscopic range finder having spaced viewing points for receiving light beams from the target being ranged, two eyepieces for binocularly viewing images of the target and means for forming in the image plane of each eyepiece two target images by light respectively from the two viewing points characterized by a central prism assembly including a polarizing beam splitter. for receiving light: from each viewing point, and f'orsp-litting, it into a first reflected beam and a second transmitted beam polarized atright angles, a quarter'wave'retardation plate and a triple mirror for receiving each of thefiist beams, for rotating their plane of pclarization through 90 degrees and foru'eflecting. them back toand through the beam splitter; a

half wavereta'rdation plate intercepting each of the second beamsfor rotating'their plane ofpolarization through 90 degrees and for transmit"- ting them respectively to the other beam splitter 8. for reflection thereat 'and for combining with the transmitted first beam in each case.

I81 An: ortho-pseudo stereoscopic range finder having spaced viewing points for receiving light beams from the target being ranged, two eyepieces for binocularly viewing images of the targetand means for forming in the image plane of each eyepiece two target images by light respectively from the two viewing points characterized by acentral prism assembly including a Porro prism for receiving light from each viewing point and for reflecting it once from the first reflecting surface of the Porro prism to the second reflecting-surface thereof, a polarizing beam splitter at-thesecond reflecting surface for splitting each beam into a first reflected beam and a second transmitted beam, the Form prisms being oriented at right angles to each other to reflect the first beams toward each other and through the other beam splitter in each case, a quarter wave retardation plate and a reflector positioned to receive each of the-second beams, to rotate their-plane of polarization through degrees and to reflect them back to the respective beam splitters whereat they are reflected and combined with the transmitted first beams and means for directing each pair of first and second beams respectively to the eyepiece image planes.

STEPHEN M. MACNEILLE.

REFERENCE S CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number. Name Date 1,062,166 Konig May 20, 1913 1,148,222 Eppenstein July 27, 1915 2,118,160 Cawley May 24, 1938 2,169,270 Pineo Feb. 6, 1940 1,305,393 Michelson June 3, 1919 2,255,631 Schulman Sept. 8. 1941 

